Summary Developmental defects are substantial contributors to morbidity and mortality in the US as well as worldwide. While considerable progress has been made to begin to understand the underlying biology that contributes to these defects, much remains poorly understood. We study morphogenesis in which cells rearrange cytoskeletal organization in response to signals from its surrounding environments. Defects in this process during embryogenesis cause birth defects and developmental problems. Our long-term goal is a more comprehensive understanding of morphogenesis: how a cell responds to signals from its environment and remodels the cytoskeleton in developing embryos where dynamic rearrangement of the cytoskeleton is the major driving force of morphogenesis. This is essential to advance our understanding of congenital and postnatal disorders in which cytoskeletal rearrangement is the underlying source of the defect. This proposed research is aimed at exploring a novel role of Erythrocyte membrane protein band 4.1 like 5 (Epb41l5) in the regulation of ciliary function. Cilia are hair like extensions from the apical surface to receive signals. Epb41l5 is a scaffold protein that mediates association of cytosolic proteins with proteins at the plasma membrane. Epb41l5 regulates a number of cellular processes that require remodeling of the actin cytoskeleton, in particular actin at the apical cortex. While previous studies reported cilia dysfunction in epb41l5 null mouse embryos, these studies concluded that the defects in cilia were secondary to defects of other Epb41l5 functions such as apical-basal polarity formation. Our preliminary data, however, suggests that Epb41l5 could have a direct role in regulating ciliary function. We established novel alleles of zebrafish epb41l5 mutants which showed normal apicobasal polarity formation but showed phenotypes associated with cilia dysfunction. We identified Nephrocystin 5 (NHPH5) as a novel Epb41l5 interacting protein. NPHP5 mutations were originally identified in patients with Nephronophthisis and NPHP5 has shown to regulate cilia function. Our hypothesis is that: Epb41l5 regulates ciliary function by inhibiting NPHP5 localization at cilia. We will test the hypothesis using mammalian cell culture system and zebrafish embryos, an established vertebrate genetic model that is accessible for experimental manipulation and imaging at all developmental stages. Completion of this study will lead to further understanding of regulatory mechanisms of ciliary function, which is necessary for developing more effective therapeutic strategies to combat ciliopathies. We believe that this study is highly cost effective and will produce data that lays the basis for a future R01.